Fluid distribution systems are designed to feed a fluid from a source to a consumption point. Each consumption point typically has a calculated and designed optimal flow or differential pressure requirement. However, depending on the type of hydronic system, the flow requirement is often variable over time and can change with factors like seasonality (e.g. summer or winter) and daily weather conditions. Specifically, the seasonality effect can lead to changes in the load at the consumption points, and may be due to factors like temperature changes in the system fluid (e.g. for heating systems), changes in demand for the system fluid (e.g. for drinking water).
Control valves are frequently used in fluid distribution systems and have a variable opening such that the flow rate can be adjusted. Specifically, control valves are provided with a moveable valve closing member inside a valve body. The opening and the closing function of the control valve can be regulated based on command signals from a thermostatic device, a sensor or a Building Management System (BMS) or the like.
The movement of a valve closing member in control valves can be operated by a pilot actuator. The pilot actuator is adapted to provide a force that can move a valve closing member inside the valve body in order to open and close the valve. A typical pilot actuator design consists of a membrane-sealed chamber, a pre-stressed spring and a fluid connection to an upstream side of the valve body. The valve closing member is retained by the force of a pre-stressed pilot spring which is typically set so that the spring urges the pilot to keep the valve open and enable a flow there through. The membrane is operationally connected to the valve closing member through a connection rod. Depending on the particular implementation, the pilot actuator and some of its components (e.g. bottom and upper chambers, disc, membrane ring, membrane, safety spring and main axis) may be quite bulky.
The pilot actuator can be used for regulating flow in both small and large fluid conduits. However, for large valves the pilot actuator needs to be of a significant size in order to provide a sufficient opening/closing force in large fluid conduits with high flow rates.